[CI] Fix SYMFONY_REQUIRE env var default value

Author: Kocal

.github/workflows/ci.yaml

@@ -83,7 +83,7 @@ jobs:
         run: |
           composer update ${{ matrix.dependency-version == 'lowest' && '--prefer-lowest' || '' }}
         env:
-          SYMFONY_REQUIRE: ${{ matrix.symfony-version || '>=5.4' }}
+          SYMFONY_REQUIRE: ${{ matrix.symfony-version || '>=6.4' }}
 
       - name: Create a new Symfony project
         run: |